Japanese beetles (JBs) are common, destructive garden pests, recognizable by their metallic green heads and coppery-brown wing covers. Adult beetles appear from early summer through August, capable of causing significant damage to over 300 plant species. Their feeding habit, known as skeletonizing, involves consuming the soft tissue between leaf veins, leaving behind a lace-like structure that quickly turns brown. Gardeners manage these pests by either repelling them from valuable plants or by choosing varieties the beetles naturally ignore.
Plants That Actively Repel Japanese Beetles
Some plants discourage Japanese beetles by emitting strong, volatile compounds that interfere with the insects’ ability to locate their preferred food sources. This olfactory disruption masks the scent of desirable host plants, causing the beetles to bypass the area. Aromatic herbs and flowers are effective because they contain natural oils and chemicals that many insects find offensive.
Plants from the Allium family, such as chives, garlic, and onions, are powerful repellents due to their high sulfur content. The pungent odor released by these plants is unappealing to the beetles, making them excellent choices for interplanting around susceptible ornamentals like roses. Catnip (Nepeta cataria) also contains the compound nepetalactone, which acts as a natural deterrent.
For defense, gardeners can strategically place these repellent plants as a perimeter or intercrop them closely with susceptible plants. Tansy (Tanacetum vulgare) is a hardy perennial whose strong aroma helps drive beetles away. White geraniums, while not strictly repellent, contain a substance that can temporarily paralyze Japanese beetles after consumption, making them easier to remove manually.
Plants Japanese Beetles Generally Avoid Feeding On
Some plants simply lack characteristics the beetles find palatable, such as soft texture or sweet scent. These resistant varieties provide a structural defense, as the beetles move on quickly after an exploratory nibble, leaving the plant largely undamaged. Choosing these plants minimizes beetle presence without relying on strong deterrents.
Many woody plants and trees are naturally avoided because their leaves are tougher or have a more leathery texture. Examples include boxwood (Buxus), junipers, and various species of oak (white, red, and scarlet). Their foliage is too difficult for the beetles to skeletonize effectively.
Ornamentals like lilac (Syringa), magnolia, and common pear are also less susceptible to damage. Their foliage may have chemical compositions or physical properties that make them undesirable for prolonged feeding. Other resistant choices include:
- Begonia
- Caladium
- Hosta
- Some conifers like fir and spruce
Using Plants for Concentrated Management
An entirely different strategy is trap cropping, which involves using certain plants to deliberately attract Japanese beetles to a specific, manageable location. The purpose is to concentrate the beetles on a “sacrifice” plant that the gardener does not mind losing, allowing for easier localized control and removal. This method exploits the beetles’ strong preference for certain plants.
Highly attractive plants like white roses, hollyhocks, and grapes are often used as trap crops because they are among the beetles’ most favored food sources. Evening primrose is an effective trap plant that can lure beetles away from more valuable specimens. The beetles aggregate on these preferred plants, making them simple to collect.
Once concentrated, the beetles can be managed by hand-picking or gently shaking the plants over a bucket of soapy water early in the morning when the insects are sluggish. This technique requires consistent monitoring and manual removal to prevent the beetles from overfeeding and moving on to other garden plants. Placing the trap crop slightly away from the protected plants ensures the beetles are drawn to the sacrifice area.